The Parents' Review
A Monthly Magazine of Home-Training and Culture
"Education is an atmosphere, a discipline, a life."
The Connection Between Geology and Scenery.
by the Rev. H. H. Moore, M.A.,
Part III. Igneous and Metaphoric Rocks.
The preceding rough sketch (see parts I. and II. in April and May, 1899) will suffice to show that the most elevated and rugged portions of our inland districts and coast line are those which are associated with the presence of igneous rocks, and of the oldest, hardest, and most metamorphosed of the sedimentary rocks. It is evident, therefore, that it must be the peculiar composition and local arrangement of those rocks that have determined the characteristic scenery of the districts where they occur. The first lesson taught by the geological evolution of the British Isles is the important part that igneous and metamorphic rocks play in forming both the framework and physiognomy of our country, and how their history has fitted them for their work. Igneous and metamorphic rocks everywhere underlie and support all the other more recent strata, and often penetrate through them and traverse them in various directions. Thus, they are like the deep foundations and thick vaulted arches that support the superstructure of our great buildings; like the iron girders and columns that bond together and give rigidity to the whole structure; like the massive breakwaters that men have piled up to oppose the violent assaults of the stormy sea. They also resemble the columns and obelisks that still stand erect amid the shapeless ruins of some ancient Egyptian temple--victorious survivors of the destructive effects of time, which has worked such ravages all around them, and yet not having won a scathless victory, but scarred all over with the marks of their fierce contest with the warring elements.
Their protective uses are illustrated in a specifically striking manner in the case of our sister isle. In regard to its physical structure, Ireland may very appropriately be compared to a saucer or plate, the flat bottom of which represents the great interior plain of carboniferous limestone, and the outer rim the almost unbroken ring of hills which surround the plain. Were it not for this natural sea wall built up of igneous, metamorphic, and other compact primary rocks, that plain would long ago have been destroyed and swallowed up by the furious waves of the Atlantic.
Having already briefly referred to the igneous, the Laurentian, the Cambrian, the Silurian, and the Devonian rocks, in connection with the localities where they are most prominent, let us now proceed to examine a little more in detail the characteristic features of the remaining formations.
The Old Red Sandstone is the next that claims our attention. This and the Devonian formation may be regarded as twins. Geologists are generally agreed that they were formed contemporaneously, but that the Old Red Sandstone rocks were lacustrine or estuarine deposits, while the Devonian rocks were their marine equivalents. As denoted by one of their titles they are chiefly arenaceous, being probably the worn materials of Silurian grits and slates, or of ancient igneous rocks, built up again in new ways. Their colour varies from a dark brick-red to brown and yellow. The redness is due to the fact that each grain of sand and marl is encrusted with a pellicle of peroxide of iron, which must have been precipitated in the waters of an inland sea or lake. The term "old" discriminates their geological position from that of a much newer series of red sandstones subsequent to the Carboniferous age. The following are the three chief divisions of the Old Red Sandstone formation:--
1. The upper or conglomerate series } Red and variegated sandstones, and quartzrose conglomerate.
2. The middle or brownstone series } Brown marly sandstones and flagstones, and thin bands or cornstones. [Cornstones are impure concretionary limestones.]
3. The lower or cornstone series } Red and grey sandstones, red and variegated marly beds, with cornstones in lower beds.
The Old Red Sandstone formation runs eastward from Milford Haven as a narrow band along the south edge of Pembrokeshire and Carnarvonshire, between the Silurian district on the north and the coal district on the south. It broadens out in Brecknockshire, Monmouthshire, and Herefordshire, running north nearly to Much Wenlock and Bridgnorth, and south nearly to Newport. Of this formation Sir Roderick Murchison wrote:--"The grandest exhibitions of the Old Red Sandstone in England and Wales appear in the escarpments of the Black Mountains in Herefordshire, and of the Vans of Brecon and Carmarthen, the one 2862 feet and the other 2000 feet above the sea. In no other part of the world visited by me have I seen such a mass of red rocks (estimated at a thickness of not less than 10,000 feet) so clearly intercalated between the Silurian and the Carboniferous strata." The summit of the Brecknock Beacons consists of the highest beds of conglomerate, which by their hardness have resisted denudation, the Carboniferous strata which once overlaid them being only just planed off. This conglomerate perhaps represents a shingly beach of an ancient Atlantic. From the neighbourhood of Three Cocks Junction and of the town of Brecon the Beacons present a very imposing appearance on account of the abruptness with which they rise to such a height, and because the rocks on the northern face of the summit form an almost precipitous escarpment over a deep cwm. The Black Mountains also form a grand feature of the scenery as one goes up the north side of the Wye valley from Hereford to Hay. They present the appearance of a huge mountain bank uplifted high above the surrounding country, and stretching many miles in length from south-east to north-west. The summit edge is almost as regular and even as the top of a table or terrace, and from it their flanks slope down a thousand feet without a break at an angle of fifty to seventy degrees. In fact, there are few escarpments in England and Wales of such length, height, and steepness, as that which runs round three sides of this elevated and extensive table-land. The height and steepness of its declivities are well shown by the profile of the bold projecting headlands with which it terminates at its north-western extremity above Hay and Talgarth. The plateau dips gradually from north-west to south-east, and in that direction streams have cut very deep, narrow, trench-like valleys. But if one would adequately appreciate the peculiar structure and scenery of the Black Mountains and the scale of their proportions, one ought at least to take the following walks over and among them. (1.) To go from Hay by New Forest Farm and climb straight up the north-western brow of the Hatteral ridge, then to go by Crib-'r-garth and the Darrens, the whole length of the ridge, keeping close to its northern edge, overlooking the deep valley in which are the headwaters of the Monnow and the villages of Craswall and Longtown. The descent should be made form its south-eastern extremity to Pandy Station. (2.) A second walk should be from Llanfihangel Station up the wild, secluded valley of the Honddhu, in which the beautiful ruins of Llanthony Priory are buried; and from the head of the valley to cross over the pass called Bwlch-y-Fingel, and to descend to Hay. (3.) A third walk should be to climb straight from Talgarth to the highest point of the ridge called Pen-y-Gader Fawr (2545 feet), from which there is a most extensive and interesting view.
These and similar walks, together with the views from the summits necessary to enable one to realize the stupendous amount of denudation which has been effected in order to sculpture these hills and the surrounding country to their present form. If we wish to restore them in imagination to their original condition, we must not only fill up with Old Red Sandstone materials the many deep valleys by which the heart of the Black Mountain plateau is furrowed, but also the depressions and vacant spaces (in some places 2000 feet deep) that now separate the Black Mountains, the Brecon and Carmarthen Beacons, the conical Sugar Loaf Mountain (1852 feet), the Blorenge Mountain, the Alp-like Skyrrid Fawr (1498 ft.)--three famous hills round about Abergavenny--also Pen-Cerrig-Calc, above Crickhowell, and many others, even including the distant Clee Hills, for there is no conclusion better established in geology than that all these hills were once united, and that they are the isolated remnants of a once continuous plateau. But this is not all: you must also pile on the top of the whole of the restored Old Red Sandstone strata a tremendous thickness of the strata belonging to the Mountain Limestone, Millstone Grit, and Coal Measures formations. On the top of the Blorenge Mountain and of Pen-Cerrig-Calc (2260 ft.), we find the uppermost beds of the Old Red Sandstone series still capped by layers of the Mountain Limestone and Millstone Grit, and at but a short distance southwards, all these strata dip under the area of the Coal Measures which escaped denudation. [Note: Of Pen-Cerrig Calc, [Daniel] Mackintosh says:--"This well-known patch is a monument of denudation perched high in the air, as if to bear witness to the extent to which elevated regions may once have been covered by deposits which have been swept clean away with the exception of a few forlorn wrecks."] The views from the Black Mountains will also show that the lower hills, the valleys, and the plains, give the measure of the denudation downwards in the different parts of the Old Red Sandstone district. Most of the hills of inferior elevation to the Black Mountains are of nearly the same height, because at the level of their present summits there were continuous beds of the harder bands of Sandstone or Cornstones, and therefore it was at this level that denudation was more successfully and generally arrested throughout a large area of Herefordshire and Monmouthshire. Of such hills the following may be mentioned as the most characteristic examples that I know:--
(1.) Dinedor Hill, crowned with a grove of trees and a Roman camp, overlooking Hereford and its Cathedral, and embracing a fine view of the Wye Valley, the Black and the Welsh Mountains. (2.) Further south is the wooded range formed by the Acornbury, Orcop, Saddlebrow, Garway, and Graig Hills. (3.) West of Hereford is Credenhill, a bold eminence thickly wooded, on the top of which is a Roman camp of 50 acres, the summer station of the troops which occupied Magna Castra (Kenchester), once an important city at its base. From its eastern edge is a fine view of the Malverns and intervening country. (4.) Still further west, the steeply scarped wooded ridge which surrounds Foxley Park, once the property and residence of Sir Uvedale Price, the great landscape gardener, and the author of the standard work, On the Picturesque. From Lady Lift, a beautiful eminence and look-out point at the south-west corner of this ridge, is a lovely view embracing the Wye Valley and the Black and Welsh Mountains. The northern edge of the same ridge overlooks Garnston Park, the quaint old town of Weobley, (5.) the peculiar pyramidal hills of Robin Hood's Butts and Canon Pyons, and (6.) the picturesque wooded group of Ivington Camp and the Dinmore Hills, between those and Leominster. (7.) The long wooded range of the Moccas Hills separating the Golden Valley from the Wye Valley, on the top of which is a fine cromlech called Arthur's Stone, and on its northern slope the well-timbered Moccas Park. (8). A similar wooded ridge divides the Golden Valley from the Escley Brook and Monnow Valleys. (9.) The Castle Frome Hills north-west of Ledbury. (10.) The Penyard Park Hills close to Ross, one of which is the huge rocking stone of Old Red conglomerate, called "The Buckstone." In most of these hills just mentioned the line at which denudation has been arrested is the line of division between the lower or Cornstone series and the middle or Brownstone series. In the cases of the Abergavenny Sugar Loaf Mountain and Skyrrid Fawr the Brownstone series have been left and the Conglomerate series have been just planed off. The plains and valleys of course are due to denudation carried deeper down into the lower division of marls and cornstones. Wherever any of the red marls and the cornstones come to the surface their decomposition produces a strong, rich, loamy soil, capable of producing heavy crops of wheat, fruit, hops, and grass. The Carselands of Gowrie, Tay and Strathearn, in Scotland are said to owe their fertility to the same formation. The red marls, whether the Old or of the New Red Sandstone formations, seem especially favourable to the production of fruit. The "apple-tree soil" of Herefordshire is a popular expression. It is a fact that the chief fruit-growing districts of our country are on the red lands of Devonshire, Herefordshire, Gloucestershire, Worcestershire, Cheshire. The Carse of Gowrie also is famous for its apples. Excepting in the districts of the Black Mountains and the Beacons, it is chiefly the beds of the middle or of the lower divisions that form the surface of the Old Red Sandstone country, to which half of Monmouthshire and the nine-tenths of Herefordshire belong. The geological conditions of such a country which have just been explained will prepare us, therefore, to expect that it will be one of undulating hills of moderate height, of well-wooded scenery, and with a soil rich in orchards, hop grounds, wheatfields, and meadows. Herefordshire is par excellence the country of the Old Red Sandstone, and everyone knows how famous it is for its beauty and fertility, for the number and productiveness of its orchards, the excellence of its cider, the fine breed of cattle reared in its rich pastures. As Professor Ramsay says:--"If anyone is desirous to realize the exquisite beauty of the scenery of the English Old Red Sandstone, let him go to the summit of the Malvern Hills, or of those above Stoke Edith, and cast his eye north and north-west, and there in far-stretching undulations of hill and dale, with towns and villages, farms and parks, he will survey a vast tract, unrivalled in varied beauty, dotted with noble wood and orchards, and fruit-trees set in every hedge, while through the fertile scene wander the Teme, the Lug, and the stately Wye, in many a broad curvature, winding its way from the Severn." If we want a striking illustration of the close dependence of the scenery and productions of a district on its geological character, it is afforded us by the great contrast experienced by passing in so short a space and time from the Silurian district of South Wales, with its bleak, rugged hills, cold grey rocks, houses and roofs of slate and flags, to the Old Red Sandstone country of Hereford, with its low, rounded hills, its warm red soil, rocks, and houses, its rich verdure, and abundant woods and orchards.
Errata--In the April number, on page 241, lines 3 and 4 from bottom should read thus:--"Carboniferous grits, alternating with slates and shales, wonderfully dislocated and contosted, form the fine cliff of Gallantry Bower and the bold headland of Hartland Point."
In the same number, on page 242, the following should have been added to the list of bays and headlands:--"The most southerly projections of the Devonshire Coast, Bolt Head, Prawle and Start Points, are composed of hard metamorphic rock, mica schists, and chlorite slate, perhaps of the Lower Silurian age. Of the two bold promontories that bound Tor Bay, Berry Head consists of the hard, highly crystalline Devonian limestone; the rocky peninsula that terminates in Hopes None, as well as the cliffs on which part of Torquay is built, consist partly of the same limestone, and partly of hard Old Red Sandstone; while the bay is eaten out of an intermediate tract of the softer New Red Sandstone."
Proofread by LNL, May 2020
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